Stage-dependent accumulation of cadmium and induction of metallothionein-like binding activity in the testis of the dogfish shark, Squalus acanthias

Cadmium (Cd) is an established spermatotoxicant. Using the shark (Squalus a canthias) testis model, we investigated stage-related patterns of intratest icular Cd accumulation and effect. After a single injection of (CdCl2)-Cd-1 09, tracer was rapidly eliminated from plasma but accumulated and was retai ned in testis for at least 7 days. intratesticular Cd-109 was stage depende nt, resulting in a 3- to 5-fold gradient: germinal zone (GZ) > premeiotic ( PrM) > meiotic (M)> postmeiotic (PoM) stages. When measured as tissue:plasm a ratios, the Cd-binding mechanism in CZ (71:1) was similar to that in live r (87:1) but lower than in kidney (381:1). The same intratesticular gradien t was seen in untreated controls when tissue Cd levels were measured by ato mic absorption spectroscopy, implying environmental exposure. A single CdCl 2 injection (5 mg/kg i.v,) elevated testicular Cd > 160-fold in all stages but did not alter the direction or magnitude of the gradient. Intratesticul ar distribution of metallothionein-like Cd-binding protein was stage depend ent (PrM = PoM > GZ = M), but the pattern differed from the Cd gradient. Th is binding component was Cd inducible in all but M stages, but induction di d not alter the stage-dependent pattern of binding activity or Cd accumulat ion. Analysis of tissue subfractions after in vivo tracer injection indicat ed that the binding mechanism responsible for the intratesticular gradient is mainly cytosolic, but that a second less abundant component is associate d with the nucleus. The functional significance of preferential Cd accumula tion in GZ and PrM stages of spermatogenesis remains to be determined.